1. Field of the Invention
The present invention is generally related to the field of microelectronics. It is related more specifically to techniques for bonding a substrate or die to a carrier as used, for instance, in microelectronics packaging and/or stacking technologies.
2. Description of the Related Technology
Substrates or dies often need to be bonded temporarily to carrier wafers, on which they may be further handled, processed or thinned. This is for instance the case when performing wafer or die thinning where the wafer or die is temporarily bonded to a carrier (typically used for extreme wafer thinning). An example of such a process can be found in U.S. Pat. No. 6,506,664, in some aspects relating to the stacking of Ultra Thin Chips.
Glue layers can be used to achieve such a temporary bond. Such glue or bonding layers need to be compatible with all processes performed on the substrate or die while it is bonded. For instance, mechanical and chemical stability is required.
When temporarily bonding a carrier to a substrate or die, depending on the glue layer (more generally bonding layer) used, the carrier can be released chemically (e.g., through etch or dissolution of the glue layer), thermally (e.g., through phase change or decomposition of the glue layer material), or under illumination (e.g., through breaking of a molecular bond).
Thermally decomposable glue layers and glue layers that are decomposable under illumination by radiation of a predetermined frequency spectrum have the advantage over chemically removable glues that carrier release is often easier or faster when compared to chemical release (especially for large bonded areas). When using a chemical release (corresponding to a chemically removable glue) the glue must be brought in contact with a chemical substance, and for large bonded areas this can occur only from the outer region inwards, resulting in a relatively slow release process.
In the embodiment of release by illumination, measures must be taken that the radiation can easily and preferably reach the glue or bonding layer with substantial uniformity, e.g., by making one of the bonded elements transparent to the radiation. Transparent should be understood as allowing enough radiation to pass through to achieve the effect of release. These insights also apply to certain embodiments.
For many thermally decomposable glue layers available today, it is very difficult or impossible to remove residues after the glue decomposition, especially without impacting the substrate or die, which is typically at least partially processed. For instance, high temperature processing such as, e.g., copper to copper thermo compression bonding, has shown to affect certain polymer glue layers, such that upon removal of this layer residues are left which are not removable or very difficult to remove.
Another technique involves the use of a sacrificial layer used for temporarily attaching the die to a carrier. The release is obtained by etching the sacrificial layer from the sides, which is however a time-consuming operation.
Document DE10320375 is related to a method for temporarily fixing two planar workpieces, e.g., a processed wafer to a glass carrier, wherein both components receive a release layer, and wherein the actual bond is established by a glue layer. The release of the workpieces takes place in a wet chemical process, wherein the release layers are dissolved and the glue layer is left over as waste.
Document US2004/0009649 is related to a method for bonding a wafer to a substrate, wherein the front surface of the wafer is temporarily attached to a support, thinned, and subsequently attached to the substrate where thereafter the support is released from the wafer surface. Optionally, a low stress material may be applied to the front surface of the wafer before attaching the wafer to the support.